Method and apparatus for use in switched capacitor systems

ABSTRACT

A system and method including a DAC that receives a multi-bit digital signal and outputs at least two analog signals including a first analog signal and a second analog signal, the first analog signal being indicative of a sum of values of bits in the multi-bit digital signal, the second analog signal also being indicative of said sum of values of said bits in the multi-bit digital signal. The first and second analog signals may be substantially equal or they may be different from each other.

TECHNICAL FIELD

This invention relates to methods and apparatus for switched capacitorsystems.

RELATED ART

Many systems employ switched capacitor techniques, for example, makinguse of capacitors and packets of charge to perform a function.

Digital to analog converters are one type of system that frequently useswitched capacitor techniques, for example as part of a digital toanalog conversion system for use in a mobile communications system.Mobile communications often include a cellular handset that uses digitalbaseband I/Q modulation and synthesis in a transmit path.

A digital-to-analog converter generates analog data in response todigital input data. One type of digital-to-analog converter receivesbinary-weighted data. Another type of digital-to-analog converterreceives equally-weighted data.

Using digital-to-analog conversion to create an analog signal oftenresults in signal noise, and/or distortion. Thus, in systems employingswitched capacitor techniques, there is often a need for a solutionwhich helps reduce noise and/or distortion. To help meet the noise anddistortion requirements, a digital to analog converter is sometimespreceded by a scrambler. Output data from a digital-to-analog convertermay be presented to a signal conditioner stage, e.g., an analog filterstage, to condition the noise and/or the distortion. One type of signalconditioner stage is a switched capacitor filter.

Analog to digital converters are another type of system that frequentlyuses switched capacitor techniques, for example as part of a digital toanalog converter used as a feedback element in a successiveapproximation type of analog to digital converter. One example of asuccessive approximation analog to digital converter is an AD574manufactured by Analog Devices, Inc.

In addition to reducing noise and/or distortion, there is often a needin switched capacitor systems to further reduce power requirements,size, and/or cost.

SUMMARY OF THE INVENTION

According to a first aspect, a DAC includes a switched capacitor networkthat receives a multi-bit digital signal, the switched capacitor networkhaving a plurality of sub DACs that each receive an associated bit ofthe multi-bit digital signal, each of the plurality of sub DACs havingan associated capacitance that receives an associated amount of chargein response to the associated bit, wherein the associated amount ofcharge for each of the plurality of sub DACs is in direct proportion toa weight of the bit, at least two of the plurality of sub DACs sharingcharge with one another, and the switched capacitor network outputs atleast one analog signal indicative of a sum of values of each bit in themulti-bit signal.

According to a second aspect, A DAC includes a switched capacitornetwork that receives an equally-weighted multi-bit digital signal andoutputs one or more analog signals, wherein at least one of the one ormore analog signals comprises a single packet of charge indicative of asum of equally weighted values of each bit in the multi-bit signal.

According to a third aspect a DAC includes a switched capacitor networkthat receives an equally-weighted multi-bit digital signal, the switchedcapacitor network having a plurality of sub DACs, at least two of theplurality of sub DACs sharing charge with one another, wherein theswitched capacitor network outputs an analog signal indicative of a sumof equally weighted values of each bit in the multi-bit signal.

According to a fourth aspect, a method of converting a multi-bit digitalsignal to an analog signal indicative of a sum of value of each bit inthe multi-bit digital signal includes charging each of a plurality ofcapacitors to a value corresponding to a value of a bit in the multi-bitsignal, wherein the charge on each capacitor corresponds to a weight ofthe value of a corresponding bit; and connecting at least two of theplurality of capacitors to one another to share charge with one another.

According to a fifth aspect, a method of converting a equally weightedmulti-bit digital signal to an analog signal indicative of a sum ofvalue of each bit in the multi-bit digital signal includes charging eachof a plurality of capacitors to a value corresponding to a value of abit in the equally-weighted multi-bit signal, and generating a singlepacket of charge on at least one capacitor indicative of a sum ofequally weighted values of each bit in the multi-bit signal.

According to a sixth aspect, a method of converting an equally weightedmulti-bit digital signal to an analog signal indicative of a sum ofvalue of each bit in the multi-bit digital signal includes charging eachof a plurality of capacitors to a value corresponding to a value of abit in the equally-weighted multi-bit signal, and connecting at leasttwo of the plurality of capacitors to one another to share charge withone another.

According to a seventh aspect, A DAC includes means for charging each ofa plurality of capacitors to a value corresponding to a value of a bitin the multi-bit signal, wherein the charge on each capacitorcorresponds to a weight of the value of a corresponding bit; and meansfor connecting at least two of the plurality of capacitors to oneanother to share charge with one another.

According to an eighth aspect, a DAC includes means for charging each ofa plurality of capacitors to a value corresponding to a value of a bitin the equally-weighted multi-bit signal, and means for generating asingle packet of charge on at least one capacitor indicative of a sum ofequally weighted values of each bit in the multi-bit signal.

According to a ninth aspect, a DAC includes means for charging each of aplurality of capacitors to a value corresponding to a value of a bit inthe equally-weighted multi-bit signal, and means for connecting at leasttwo of the plurality of capacitors to one another to share charge withone another.

According to a tenth aspect, an integrated circuit includes anintegrated switched capacitor network that receives a multi-bit digitalsignal, the switched capacitor network having a plurality of sub DACsthat each receive an associated bit of the multi-bit digital signal,each of the plurality of sub DACs having an associated capacitance thatreceives an associated amount of charge in response to the associatedbit, wherein the associated amount of charge for each of the pluralityof sub DACs is in direct proportion to a weight of the bit, at least twoof the plurality of sub DACs sharing charge with one another, and theswitched capacitor network outputs at least one analog signal indicativeof a sum of values of each bit in the multi-bit signal.

According to an eleventh aspect, an integrated circuit includes anintegrated switched capacitor network that receives an equally-weightedmulti-bit digital signal and outputs one or more analog signals, whereinat least one of the one or more analog signals comprises a single packetof charge indicative of a sum of equally weighted values of each bit inthe multi-bit signal.

According to a twelfth aspect, an integrated circuit includes anintegrated switched capacitor network that receives an equally-weightedmulti-bit digital signal, the switched capacitor network having aplurality of sub DACs, at least two of the plurality of sub DACs sharingcharge with one another, wherein the switched capacitor network outputsan analog signal indicative of a sum of equally weighted values of eachbit in the multi-bit signal.

According to a thirteenth aspect, a system includes a DAC that receivesa multi-bit digital signal and outputs at least two analog signals eachindicative of a sum of values of bits in the multi-bit digital signal;and a signal conditioning stage that receives at least two of the atleast two analog signals.

According to a fourteenth aspect, a system includes a DAC that receivesdigital input signals at an input data rate and outputs analog signalsindicative of the digital signals to a signal conditioning stage at anoutput data rate different than the input data rate.

According to a fifteenth aspect, a method includes receiving a multi-bitdigital signal, generating at least two analog output signals eachindicative of a sum of values of bits in the multi-bit digital signal;and filtering at least two of the at least two analog output signals.

According to a sixteenth aspect, a system includes means for receiving amulti-bit digital signal, means for generating at least two analogoutput signals each indicative of a sum of values of bits in themulti-bit digital signal; and means for filtering at least two of the atleast two analog output signals.

According to a seventeenth aspect, a system includes a DAC that receivesa multi-bit digital signal and outputs at least two analog signals eachindicative of a sum of values of bits in the multi-bit digital signal.

According to eighteenth aspect, a method includes receiving a multi-bitdigital signal, and generating at least two analog output signals eachindicative of a sum of values of bits in the multi-bit digital signal.

According to an eighteenth aspect, a system includes means for receivinga multi-bit digital signal, and means for generating at least two analogoutput signals each indicative of a sum of values of bits in themulti-bit digital signal.

According to a nineteenth aspect, a switched capacitor filter has afirst switched capacitor comprising a switched capacitor withoutsubstantial effects from parasitic characteristics, and a secondswitched capacitor in parallel with the first switched capacitor, thesecond switched capacitor having effects from parasitic characteristics.

According to a twentieth aspect, a system includes a switched capacitorfilter having a first switched capacitor comprising a switched capacitorand a second switched capacitor in parallel with the first switchedcapacitor, the second switched capacitor having characteristicsincluding parasitic effects; and a DAC having a switched capacitorhaving characteristics including parasitic effects substantiallycorresponding to the parasitic effects of the second switched capacitorof the switched capacitor filter.

According to a twenty first aspect, an apparatus includes a firstswitched capacitor cell having a reference direction and being adaptedto electrically connect to a second switched capacitor cellsubstantially identical to the first switched capacitor cell, the secondswitched capacitor cell having a reference direction and being orientedsuch that the reference direction of the second switched capacitor cellis directed in substantially the same direction as the referencedirection of the first switched capacitor cell, and being adapted toelectrically connect to a third switched capacitor cell substantiallyidentical to the first switched capacitor cell, the third switchedcapacitor cell having a reference direction and being oriented such thatthe reference direction of the third switched capacitor cell is directedin direction angularly offset from the direction in which the referencedirection of the first switched capacitor cell is directed.

According to a twenty second aspect, a system includes a binary weightedDAC; and a segmented DAC, coupled to the binary weighted DAC, thesegment DAC comprising a switched capacitor network that receives amulti-bit digital signal, the switched capacitor network having aplurality of sub DACs that each receive an associated bit of themulti-bit digital signal, each of the plurality of sub DACs having anassociated capacitance that receives an associated amount of charge inresponse to the associated bit, at least two of the plurality of subDACs sharing charge with one another, and the switched capacitor networkoutputs at least one analog signal indicative of a sum of values of eachbit in the multi-bit signal.

According to a twenty-third aspect, a system includes a scrambler thatreceives input and provides output; and a switched capacitor DAC thathas a plurality of capacitors and redistributes charge between at leasttwo of the plurality of capacitors, coupled to the scrambler, thatreceives digital output of the scrambler.

According to a twenty fourth aspect, a system includes a digital toanalog converter that receives a multi-bit digital signal and producesan analog output that is proportional to the square of the multi-bitdigital signal.

According to a twenty-fifth aspect of the invention, an analog todigital converter has an analog comparison stage coupled to a digitallatch stage, the analog to digital converter including a feedbackelement through which an output of the digital latch stage is fed backto an input of the analog comparison stage, wherein the feedback elementincludes a digital to analog converter.

According to a twenty sixth aspect of the invention, a method for use inan analog to digital converter having an analog comparison stage coupledto a digital latch stage includes coupling an output of the digitallatch stage back to an input of the analog comparison stage through adigital to analog converter that receives a multi-bit digital signal andproduces an analog output proportional to the square of the multi-bitdigital signal.

According to a twenty seventh aspect of the invention, a handset for amobile communication system includes an input stage that receives aninput signal and outputs a multi-bit digital signal to adigital-to-analog conversion system that receives the multi-bit digitalsignal and outputs an analog signal indicative of a sum of values ofbits in the multi-bit signal, and including a switched capacitor networkthat receives a multi-bit digital signal, the switched capacitor networkhaving a plurality of sub DACs that each receive an associated bit ofthe multi-bit digital signal, each of the plurality of sub DACs havingan associated capacitance that receives an associated amount of chargein response to the associate bit, wherein the associated amount ofcharge for each of the plurality of sub DACs is in direct proportion toa weight of the bit, at least two of the plurality of sub DACs sharingcharge with one another, and the switched capacitor network outputs atleast one analog signal indicative of a sum of values of bits in themulti-bit signal.

According to a twenty eighth aspect, a system includes a digital signalprocessing stage that receives input and provides output; and a switchedcapacitor DAC that has a plurality of capacitors and redistributescharge between at least two of the plurality of capacitors, coupled tothe digital signal processing stage, that receives digital output of thedigital signal processing stage.

According to a twenty ninth aspect, a digital to analog converterreceives a first multi-bit digital signal and a second multi-bit digitalsignal, and produces an analog output that is indicative a product ofthe first multi-bit digital signal and the second multi-bit digitalsignal.

According to a thirtieth aspect, in an analog to digital converterhaving an analog comparison stage coupled to a digital latch stage, afeedback element through which an output of the digital latch stage iscoupled back to an input of the analog comparison stage, wherein thefeedback element includes a digital to analog converter that receives afirst multi-bit digital signal and a second multi-bit digital signal,and produces an analog output that is indicative of a product of thefirst multi-bit digital signal and the second multi-bit digital signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of a portion of a handsetfor a mobile communication system that includes a digital-to-analogconversion system;

FIG. 2 is a block diagram of one embodiment of the digital-to-analogconversion system of FIG. 1 and including a DAC portion with two DACstages;

FIG. 3 is a block diagram of one embodiment of the DAC stage of FIG. 2that includes a switched capacitor DAC;

FIG. 4 is a block diagram of one embodiment of the switched capacitorDAC of FIG. 3;

FIG. 5 is a block diagram of one embodiment of the switched capacitorDAC of FIG. 4 that is adapted to convert a four-bit digital input signalinto a corresponding analog signal;

FIG. 6 illustrates one embodiment of a non-overlapping three phase clockused in the operation of the switched capacitor DAC of FIGS. 7A-7C;

FIGS. 7A-7C are block diagrams showing the operation of the switchedcapacitor DAC of FIG. 5 for each of three clock phases of anon-overlapping three phase clock;

FIGS. 8A-8D are block diagrams showing the operation of anotherembodiment of the switched capacitor DAC for each of four phases of anon-overlapping four phase clock;

FIG. 9 shows one embodiment of a non-overlapping four phase clock usedin the operation of the switched capacitor DAC of FIG. 8A-8D;

FIG. 10 shows the operation of the switched capacitor DAC of FIGS. 7A-7Con one phase of a non-overlapping four phase clock;

FIGS. 11A-11D are block diagrams showing the operation of anotherembodiment of the switched capacitor DAC of FIG. 5 for each of fourphases of a non-overlapping four phase clock;

FIGS. 12A-12C are block diagrams showing the operation of anotherembodiment of the switched capacitor DAC of FIG. 5 for each of the threeclock phases of a non-overlapping three phase clock;

FIG. 13 is a schematic diagram of another embodiment of the switchedcapacitor DAC of FIG. 4;

FIGS. 14A-14C are block diagrams showing the operation of the switchedcapacitor DAC of FIG. 13;

FIG. 15 is a block diagram of another embodiment of the switchedcapacitor DAC of FIG. 4;

FIG. 16A shows a schematic diagram of another embodiment of the one-bitDAC of the switched capacitor DAC of FIG. 13;

FIG. 16B shows a schematic diagram representative of one embodiment of aswitched capacitor cell which may for example be used in forming aswitched capacitor DAC;

FIG. 16C shows a schematic diagram of one embodiment of two switchedcapacitor cells to be interconnected;

FIG. 16D shows a schematic diagram of one embodiment of two switchedcapacitor cells to be oriented substantially perpendicular to oneanother and interconnected;

FIG. 16E shows a schematic diagram of one embodiment of four switchedcapacitor cells to be interconnected in a ring arrangement;

FIG. 17 shows one embodiment of a DAC formed in part by the switchedcapacitor cells of FIG. 16E;

FIG. 18 shows an embodiment of a switched capacitor DAC adapted toconvert a binary weighted input signal into a corresponding analogsignal;

FIGS. 19A-19C are block diagrams showing the operation of the switchedcapacitor DAC of FIG. 18;

FIG. 20 is a block diagram of one embodiment of the DAC portion of FIG.3;

FIG. 21 is a schematic diagram representative of one embodiment of theDAC portion shown in FIG. 20;

FIG. 22 is a schematic diagram representative of another embodiment ofthe DAC portion shown in FIG. 20;

FIG. 23 is a block diagram of another embodiment of the DAC stage ofFIG. 2 that includes a scrambler;

FIG. 24 is a block diagram of one embodiment of a four bit scrambler;

FIG. 25 is a schematic diagram representation of one embodiment of theDAC portion shown in FIG. 20;

FIG. 26 is a schematic block diagram of another embodiment of the DACstage of FIG. 2;

FIG. 27 is a schematic diagram of one embodiment of a portion of the DACstage of FIG. 2 in combination with one embodiment of the switchedcapacitor filter stage of FIG. 2;

FIG. 28A is an illustration of a top view of one embodiment of aswitched capacitor cell;

FIG. 28B is an illustration of a top view of another embodiment of aswitched capacitor cell;

FIG. 29 is a representation of a top view of one embodiment of a dielayout of a DAC portion having a plurality of SC cells;

FIG. 30 is a schematic diagram of one embodiment of the continuous timefilter stage of FIG. 2;

FIG. 29 shows a schematic diagram of another embodiment of the switchedcapacitor DAC of FIG. 4;

FIG. 30 shows schematic diagrams of one embodiment of the continuoustime filter stage of FIG. 2; and

FIG. 31 is a block diagram of one embodiment of a squaring circuit;

FIG. 32 shows a three phase clock;

FIGS. 33A-33C are block diagrams showing operation of one embodiment ofthe squaring circuit of FIG. 32;

FIGS. 34A-34C are block diagrams showing operation of one embodiment ofthe squaring circuit of FIG. 32; and

FIG. 35 is a block diagram of one embodiment of an analog to digitalconverter.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of one embodiment of a portion of a handset 50for a mobile communication system. The handset 50 includes an inputportion 52 having a transducer 54 that receives an input signal 56,e.g., a voice or other acoustical signal, representing information to becommunicated via the mobile communication system. The transducer 54converts the input signal 56 into an electrical signal, typically ananalog signal, which is supplied to an analog-to-digital converter (ADC)58, for example a voiceband ADC. The ADC 58 periodically samples theelectrical signal and generates a sequence of multi-bit digital signals,which are supplied to a digital baseband processor 60. The basebandprocessor 60 performs further signal processing, including for example,compression. The output of the baseband processor 60 is supplied toburst store stage 62, which feeds a GMSK modulator 64. The GMSKmodulator 64 produces multi-bit digital signals, which is supplied viasignal lines, represented by a signal line 66, to a digital to analogconversion system (DAC) 68. The digital to analog conversion system 68converts the sequence of multi-bit digital signals into an analogsignal, which is supplied via signal line 70 to an output portion 72.The output portion 72 includes a mixer 74 that receives the analogsignal on signal line 70 and feeds a transmitter 76, which in turntransmits the signal. DAC can be used in any digital to analogconversion.

FIG. 2 is a block diagram of one embodiment of the digital to analogconversion system 68, which utilizes a differential I/Q configuration.An I channel 78 of the digital to analog conversion system 68 includes ablock 80 that receives the sequence of multi-bit digital signals onsignal line 66. The block 80 generates two sequences of multi-bitdigital signals, i.e., a first sequence of multi-bit digital signalsthat is output on signal line 82, and a second sequence of multi-bitdigital signals that is output on signal line 84. The second sequence ofmulti-bit digital signals is generated to be the complement of the firstsequence of multi-bit digital signals. The first sequence of multi-bitdigital signals represents a positive version of the input signal. Thesecond sequence of multi-bit digital signals represents a negativeversion of the input signal.

The first sequence of multi-bit digital signals is supplied to a firstdigital to analog converter stage 86, which generates analog signalsthat correspond to the first sequence of multi-bit digital signals. Thesecond sequence of multi-bit digital signals is supplied to a seconddigital to analog converter stage 88, which generates analog signalsthat correspond to the second sequence of multi-bit digital signals. Theanalog signals from the first and the second DAC stages 86, 88 may besupplied to signal conditioning stage 89 that may comprise an analogfilter, for example, a switched capacitor (SC) filter stage 90, whichmay help attenuate noise and/or distortion components of the analogsignals. The SC filter 90 feeds a differential analog signal to thecontinuous time (CT) filter stage 92, which further attenuates noiseand/or distortion. The CT filter stage 92 passes a differential analogsignal to a pad driver stage 94. The CT filter stage 92 has a firstoutput that connects via a first resistor 96 to a first pad 98. The CTfilter stage 92 has a second output that connects via a second resistor100 to a second pad 102. A capacitor 104 has a first terminal connectedto the first pad 98, and a second terminal connected to the second pad102.

A Q channel 106 of the digital to analog conversion system 68 containssubstantially the same components as the I channel 78.

The output data rate from each of the DAC stages is typically the sameas the input sample rate of the SC filter. However, as is explainedhereinbelow, in the present system, the DAC stages may or may notoperate at the same clock frequency as the SC filter stage. For example,one embodiment of the mobile communication system uses a system clockrunning at 13 MHz, wherein the output data rate from the GMSK modulatoris 6.5 MHz, the cycle frequency of each of the DAC stages is 6.5 MHz,and the input sample rate of the SC filter stage 90 is 13 MHz.

FIG. 3 is a block diagram of one embodiment of the DAC stage 86, whichreceives a binary-weighted multi-bit digital signal on signal lines 82.The binary-weighted multi-bit digital signal is divided into abinary-weighted LSB portion and a binary-weighted MSB portion. In oneembodiment, for example, the binary weighted multi-bit digital signal isten bits, the MSB portion is four bits, and the LSB portion is six bits.The LSB's are supplied to a switched capacitor (SC) DAC 108 of a DACportion 110 of the DAC stage 86. The SC DAC 108 forms an analog signalcorresponding to the value represented by the LSB's. The MSB's aresupplied to a digital signal processing stage 109 having a thermometerencoder 112 that converts the MSB's into an equally-weighted multi-bitdigital signal. The equally-weighted multi-bit digital signal is inputto a switched capacitor (SC) DAC 114, of the DAC portion 110 of the DACstage 108. The SC DAC 114 is referred to herein as a segmented SC DACbecause it forms an analog signal corresponding to the value representedby the equally-weighted multi-bit digital signal. The analog signal fromthe SC DAC 108 and the analog signal from the segmented SC DAC 114 aresummed at 118 to form an analog signal, output on signal line 120. Inone embodiment of the handset, the DAC stage generates 6.5 millionsamples per second (MS/s).

FIG. 4 is a block diagram of one embodiment of a SC DAC 150 that may beused to form one or both of the SC DAC 108 and the SC DAC 114 in thehandset 50. The SC DAC 150 receives a multi-bit digital signal, e.g.,bit₁₋bit_(n). Each bit has an associated weight,weight_(bit1)-weight_(bitN). In one embodiment, the weight of each bitis different than those of the other bits. For example, bit₁-bit_(N) mayrepresent binary-weighted bits. In another embodiment, bit₁₋bit_(N) areequally-weighted, and all of the weights, i.e.,weight_(bit1)-weight_(bitN), are the same.

The SC DAC includes a plurality of switched capacitor sub-DACs (SCsub-DACs) further described hereinbelow. Each of the SC sub-DACs sharescharge via a charge sharing network with at least one other of the SCsub-DACs. The SC DAC 150 outputs one or more analog signals, e.g.,output₁-output_(M), each indicative of a sum of values of the bits inthe multi-bit signal.

FIGS. 5, 7A-7C, 8A-8C, 10, 11A-11D, 12A-12C, 13, 17, 14A-14C, 15, 20,21, 22, 25, disclose various embodiments of the SC DAC 150.

Referring now to FIG. 5, a block diagram shows one embodiment of the SCDAC 150 that is adapted to convert a 4-bit digital input signal bit₁,bit₂, bit₃, bit₄, into a corresponding analog signal, which is suppliedto output terminal 160. The DAC 150 comprises four switched capacitorDACs 162, 164, 166, 168, sometimes referred to as sub-DACs. In thisembodiment, each of the sub-DACs 162, 164, 166, 168 is a one bit DAC.

The one-bit DAC 162 has a reference voltage V1 connected to a firstterminal of a switch S1, the second terminal of which is connected to afirst terminal of a switch S2 and a first terminal of a switch S3. Asecond terminal of the switch S2 is connected to a reference voltage V2.A second terminal of the switch S3 is connected to a first terminal of acapacitor C1 that has a second terminal connected to a referencevoltage, e.g., ground. The digital signal bit₁ is presented to an inputterminal 172 from where it is supplied to the one-bit DAC 162 to controlthe “on” (i.e., closed)/“off” (i.e., open) condition of the switch S1.The digital signal bit₁ is further supplied to an inverter 174 thatgenerates a signal at terminal 176 used to control switch S2.

The one-bit DAC 164 has a reference voltage V3 connected to a firstterminal of a switch S4, the second terminal of which is connected to afirst terminal of a switch S5 and a first terminal of a switch S6. Asecond terminal of the switch S5 is connected to a reference voltage V4.A second terminal of the switch S6 is connected to a first terminal of acapacitor C2 having a second terminal connected to a reference voltage,e.g., ground. The digital signal bit₂ is presented to an input terminal178 from where it is supplied to the one-bit DAC 164 to control switchS4 and input to an inverter 180 that generates a signal at terminal 182used to control switch S5.

The one-bit DAC 166 has a reference voltage V5 connected to a firstterminal of a switch S7, the second terminal of which is connected to afirst terminal of a switch S8 and a first terminal of a switch S9. Asecond terminal of the switch S8 is connected to a reference voltage V6.A second terminal of the switch S9 is connected to a first terminal of acapacitor C3 having a second terminal connected to a reference voltage,e.g., ground. The digital signal bit₃ is presented to an input terminal184 from where it is supplied to the one-bit DAC 166 to control switchS7 and input to an inverter 186 that generates a signal at terminal 188used to control switch S8.

The one-bit DAC 168 has a reference voltage V7 connected to a firstterminal of a switch S10, the second terminal of which is connected to afirst terminal of a switch S11 and a first terminal of a switch S12. Asecond terminal of the switch S11 is connected to a reference voltageV8, a second terminal of the switch S12 is connected to a first terminalof a capacitor C4 having a second terminal connected to a referencevoltage, e.g., ground. The digital signal bit₄ is presented to an inputterminal 190 from where it is supplied to the one-bit DAC 168 where itis used to control charging switch S10 and input to an inverter 192 thatgenerates a signal at terminal 194 used to control switch S11.

The first terminal of each of the capacitors C1, C2, C3, C4 is suppliedto a first terminal of a charge sharing switch S13, charge sharingswitch S14, charge sharing switch S15, and charge sharing switch S16,respectively. The second terminal of each of the switches S13-S16 areconnected to a first terminal of a charging switch S17, that has asecond terminal connected to the output terminal 160.

In one embodiment, each of the digital signals bit₁, bit₂, bit₃, andbit₄ are equally-weighted. In such an embodiment, the one-bit DAC 162,the one-bit DAC 164, the one-bit DAC 166, and the one-bit DAC 168 mayhave similar configurations wherein, V1=V3=V5=V7, V2=V4=V6=V8, and thevalues of C1, C2, C3, and C4 are identical, or at least substantiallyidentical. However, such similarity is not absolutely required. In otherequally-weighted embodiments, the one-bit DAC 162, the one-bit DAC 164,the one-bit DAC 166 and the one-bit DAC 168 may not be identical. Eachof the switched capacitor sub-DACs employs charge approximately equal toa constant K, times a weight(s) of the bit(s) into the switchedcapacitor sub-DAC.

In one embodiment, the reference voltages V1, V3, V5 and V7 areconnected to a reference voltage V_(ref) (not shown), and referencevoltages V2, V4, V6, V8 are connected to ground.

The DAC 150 may receive a non-overlapping 3-phase clock, P1, P2, P3,shown in FIG. 6. The closed/open condition of the switches S3, S6, S9,and S12 is controlled by the P3 signal of the 3-phase clock. The P1signal of the 3-phase clock controls the open/closed condition of thecharge sharing switches S14, S15, and S16. The P2 signal of the 3-phaseclock controls the open/closed condition of the switch S17. Thelogical-OR of the P1 and P2 signals, P1+P2, controls the open/closedcondition of the switch S13. That is, S13 closes when either P1 or P2 isin a logical high state.

In particular, on clock phase P3, i.e., phase P3 has a logic high state(e.g. “1”), capacitors C1, C2, C3, and C4 are each charged to V_(ref)or, alternatively, discharged to ground in response to the state of theassociated one of the digital signals bit₁, bit₂, bit₃, bit₄, and chargesharing switches S13, S14, S15, and S16 and output switch S17, are allin the open condition. On clock phase P1, charging switches S3, S6, S9,and S12 are all in an open condition, and charge sharing switches S13,S14, S15 and S16 are all in a closed condition, wherein charge may beredistributed. On clock phase P2, all charging switches, i.e., S3, S6,S9, and S12, and charge sharing switches S14, S15, and S16, are in anopen condition. Also on phase P2, charge sharing switch S13 and outputswitch S17 are each in a closed condition wherein charge may bedelivered to the output terminal 160.

FIGS. 7A-7C are block diagrams showing the operation of the SC DAC 150of FIG. 5 for each of the 3 clock phases in the event that inputterminals 172, 178, 184, and 190 are supplied with digital bit signalsbit₁, bit₂, bit₃, bit₄, having logic states of 1, 0, 0, 0, respectively.Tables show the relationship between the clock phase, and the state(i.e., voltage and charge) of the capacitors in the one-bit DACs. InFIG. 7 and similarly labeled figures, the charges Q(C1) . . . Q(CN)represent the charge on capacitors C1 . . . CN, respectively. Referringnow to FIG. 7A, on phase P3 of the 3-phase clock, all of the chargesharing switches S13, S14, S15, and S16 and the output switch S17, arein the open condition. The capacitor C1 is charged to V_(ref) inresponse to the logic state 1 on terminal 172. Capacitors C2, C3 and C4are all discharged to ground in response to the logic state 0 signals onterminals 178, 184, 190, respectively. Referring now to FIG. 7B, onphase P1 of the 3-phase clock, all of the charging switches S3, S6, S9and S12 (FIG. 5) and the output switch S17 are in an open condition, andall of the charge sharing switches S13, S14, S15 and S16 are in a closedcondition, whereby charge is redistributed and resulting in the totalcharge on all of the capacitors being divided among all of thecapacitors. If the capacitors C1, C2, C3, C4 all have the samecapacitance value C, then the charge is shared equally so that thevoltage across each capacitor becomes V_(ref)/4. Referring now to FIG.7C, on phase P2, charge sharing switches S14, S15, and S16 are in theopen condition, output switch S17 is in the closed condition, andcapacitor C1 (FIG. 5) of one-bit DAC 162 delivers its charge to theoutput terminal 160. On the next occurrence of phase P3 (not shown), themulti-bit digital signal bit₁, bit₂, bit₃, and bit₄ may be updated andprovided to the DAC 150 via input terminals 172, 178, 184, 190.

In one or more embodiments charge sharing (i.e., mixing) beforedelivering may help reduce non-linear glitch energy. However, areduction in glitch energy need not be sought nor obtained in everyembodiment, and is not a requirement of the switched capacitortechniques disclosed herein.

The accuracy of the signal(s) out of the SC DAC 150 depends at least inpart on the degree of correspondence between the capacitors C1, C2, C3,C4. In some embodiments it may be sought to have the components that areused to employ the switched capacitor techniques, e.g., C1, C2, C3, C4,match as closely as is possible limited only for example by limitationsin manufacturing processes. In other embodiments however, such matchingmay not be required or desired, but rather, all that may be desired is adegree of correspondence to provide suitable DAC transfercharacteristics. Thus, in some embodiments they may be substantiallyidentical, but in other embodiments they may not be substantiallyidentical.

In some embodiments, there may be one or more parasitic capacitance(s)that have an effect on the degree of correspondence, and it may bedesirable, although not necessary to the techniques described herein, toprovide a parasitic capacitance(s) that has an effect that offsets aneffect of other parasitic capacitance.

The term switch as used herein is defined as any type of switchingelement. The term capacitor as used herein is defined as any type ofcapacitive element. The switches and the capacitors are not limited toany particular type(s) of switching element and capacitive element,respectively. Thus for example, a switching element may be a singleelement. As another example, a switching element may comprise aplurality of elements that function as a switch. As a further example, acapacitive element may be a capacitor. As a further example, acapacitive element may comprise one or more elements that providecapacitance.

A switch may include but is not limited to one or more active elements(for example one or more transistors) and may but need not employ MOStechnology. A capacitor may include but is not limited to metal,polysilicon and double polysilicon, metal metal, metal poly, polydiffusion, semiconductors, junction capacitors, parallel platetechnology, adjacent conductors, fringing capacitors.

Although described above with respect to an input signal having logicstates of 1, 0, 0, 0, the input signals can have logic states with anycombination of ones and zeros.

In another embodiment, the digital signal bit₁, bit₂, bit₃, and bit₄ arebinary-weighted bit signals. In such embodiment, the weight of thedigital bit signals bit₁, bit₂, bit₃, and bit₄ are 1, 2, 4, and 8,respectively. To accommodate these various weights, each of the SC DACsutilize an amount of charge proportional to the weight of the bit signalsupplied to the SC DAC. Thus, C1 is provided with ½ of the chargeprovided to C2, ¼ of the charge provided to C3, and ⅛ of the chargeprovided to C4. In other words, the charge provided to C4 is 8 timesthat provided to C1, 4 times that provided to C2, and 2 times thatprovided to C3. On clock phase P1, switches S13-S16 are in the closedcondition, whereby charge is redistributed among the capacitors so thatthe voltage across each of the capacitors is indicative of the sum ofthe values of the bits in the multi-bit signal. The charge on eachcapacitor is equal to the voltage across that capacitor multiplied byits capacitance. On the phase P2, the output switch S17 is in the closedcondition and one of the capacitance delivers its charge to the outputterminal.

In one embodiment, the SC DAC 108 (FIG. 3) is formed using a SC DAC 150,where the size of each capacitor C1, C2, C3, C4 of the one-bit DACs 162,164, 166, 168, respectively, is scaled directly proportionate to theweight of the binary-weighted bit input to the one-bit DACs 162, 164,166, 168.

FIGS. 8A-8D are block diagrams showing the operation of anotherembodiment of the SC DAC 150, for each of 4 phases of a non-overlappingfour phase clock (FIG. 9) if input terminals 172, 178, 184, 190, aresupplied with digital bit signals bit₁, bit₂, bit₃, bit₄, having logicstates of 1, 0, 0, 0, respectively. Tables show the relationship betweenthe clock phase and the state (i.e., voltage and charge) of thecapacitors in the one-bit DACs. The non-overlapping four phase clock maybe derived from a master clock (FIG. 9). The embodiment shown in FIGS.8A-8D is the same as that shown in FIG. 5 and FIGS. 7A-7C, except thatswitches S18-S24 replace switches S13-S17. Referring now to FIG. 8A, onphase P3 of the 4-phase clock, capacitor C1 of the one-bit DAC 162 ischarged to a voltage V_(ref) in response to the logic state 1 on inputterminal 172. Capacitors C2, C3, and C4 of the one-bit DACs 164, 166,168, respectively, are all discharged to ground in response to the logicstate 0 on each of the input terminals 178, 184, 190. All of the chargesharing switches S18-S23 and the output switch S24 are in the opencondition. Referring now to FIG. 8B, on phase P4 of the 4-phase clock,charge sharing switches S18, S19, S20, and S21 are in the closedcondition wherein the charge on capacitor C1 (FIG. 5) of the one-bit DAC162 is redistributed. Capacitor C1 retains ½ of the charge and capacitorC2 (FIG. 5) of one-bit DAC 164 receives ½ of the charge. In the eventthat either capacitor C3 or capacitor C4 had charge, the charge would beredistributed between capacitor C3 and capacitor C4.

Referring now to FIG. 8C, on phase P1 of the 4-phase clock, chargesharing switches S19 and S21 are in an open condition. Charge sharingswitches S22 and S23 are in a closed condition, the charge on capacitorC1 of the one-bit DAC 162 is redistributed between capacitor C1 andcapacitor C3 of the one-bit DAC 166. In particular, in one embodimentthe charge on the capacitor C1 is divided substantially evenly betweencapacitor C1 and capacitor C3 such that each ends up with substantiallyone half of the charge on capacitor C1 in FIG. 8B, i.e., one quarter ofthe total charge on capacitor C1 in FIG. 8A. Referring now to FIG. 8D,on phase P2 charge sharing switches S19, S20, S21, and S23 are in anopen condition. Also on phase P2 switches S18, S22, and S24, are in aclosed condition whereby capacitor C1 (FIG. 5) of the one-bit DAC 162delivers its charge to the output terminal 160.

Referring now to FIG. 10, in another embodiment, the SC DAC 150described with respect to FIGS. 7A-7C operates with a non-overlappingfour-phase clock, e.g., the four-phase clock illustrated in FIG. 9instead of the three-phase clock of FIG. 6. On phase P3 of thefour-phase clock, the condition of the SC DAC 150 is the same as thatdescribed above with respect to FIG. 7A. On phase P4 of the four-phaseclock, the condition of the SC DAC 150 is the same as that describedabove with respect to FIG. 7B. On phase P1 of the four-phase clock, thecondition of the SC DAC 150 is the same as that described above withrespect to FIG. 7C. FIG. 10 shows the state of the SC DAC 150 on phaseP2 of the four-phase clock. On phase P2 of the four-phase clock, thecharging switches S3, S6, S12 (FIG. 5) are in the open condition,charge-sharing switches S13, S15, S16 are in the open condition, andswitch S14 and output switch S17 are in the closed condition, wherein C2of the one-bit DAC delivers its charge to the output terminal 160. Thus,in such embodiment, two copies, each indicative of the sum of the valuesof the bits in the multi-bit digital input signal, are separatelydelivered to the output terminal. As described above, in thisembodiment, they are delivered one after the other. However, in anotherembodiment, they may be delivered simultaneously.

FIGS. 11A-11D are block diagrams showing the operation of the embodimentof FIG. 5 for each of 4 phases of a non-overlapping four phase clock(FIG. 9) if input terminals 172, 178, 184, 190, are supplied withdigital bit signals bit₁, bit₂, bit₃, bit₄, having logic states of 1, 0,0, 0, respectively. Tables show the relationship between the clock phaseand the state (i.e., voltage and charge) of the capacitors in theone-bit DACs. The embodiment shown in FIGS. 11A-11D is the same as thatshown in FIG. 5 and FIGS. 7A-7C, except that switches S18-S27 replaceswitches S13-S17.

Referring now to FIG. 11A, on phase P3 of the 4-phase clock, capacitorC1 of the one-bit DAC 162 is charged to a voltage V_(ref) in response tothe logic state 1 on input terminal 172. Capacitors C2, C3, and C4 ofthe one-bit DACs 164, 166, 168, respectively, are all discharged toground in response to the logic state 0 on each of the input terminals178, 184, 190. All of the charge sharing switches S18-S21, S25-S27 arein the open condition. Referring now to FIG. 11B, on phase P4 chargesharing switches S18, S19, S20, and S21 are in a closed conditionwherein the charge on capacitor C1 (FIG. 5) of the one-bit DAC 162 isredistributed, whereby capacitor C1 retains ½ of the charge andcapacitor C2 (FIG. 5) of one-bit DAC 164 receives ½ of the charge. Inthe event that either capacitor C3 or capacitor C4 had charge, thecharge would be redistributed between capacitor C3 and capacitor C4.

Referring now to FIG. 11C, on phase P1, charge sharing switches S19 andS21 are in an open condition and charge sharing switch S26 is in aclosed condition. The charge on capacitor C1 of the one-bit DAC 162 isredistributed between capacitor C1 and capacitor C3 of the one-bit DAC166. In particular, the charge on the capacitor C1 is dividedsubstantially evenly between capacitor C1 and capacitor C3 such thateach ends up with ½ the charge on capacitor C1 in FIG. 11B, i.e., ¼ ofthe total charge on capacitor C1 in FIG. 11A. Referring now to FIG. 11D,on P2 charge sharing switches S19, S20, S21, S26, and S27, are in anopen condition, and switches S18, and S25, are in the closed conditionwhereby capacitor C1 of the one-bit DAC 162 (FIG. 5) delivers its chargeto the output terminal 160. Although switch S27 is in an open conditionon phase P2 and does not deliver charge, in other embodiments, switchS27 may be configured to be in a closed condition on phase P2 so thatswitch S27 delivers a copy of the charge, which is in addition to thecopy delivered by switch S25. In still further embodiments, anadditional clock phase, e.g., a phase P5, is provided and switch 27 isused to deliver a copy of the charge on phase P5.

FIGS. 12A-12C are block diagrams showing the operation of anotherembodiment of the SC DAC 150 of FIG. 5 for each of the 3 clock phases ifinput terminals 172, 178, 184, and 190 are supplied with digital bitsignals bit₁, bit₂, bit₃, bit, having logic states of 1, 0, 0, 0,respectively. Tables show the relationship between the clock phase andthe state (i.e., voltage and charge) of the capacitors in the one-bitDACs. The embodiment shown in FIGS. 12A-12C is the same as that shown inFIG. 5 and FIGS. 7A-7C, except that switches S28-S33 replace switchesS13-S17. Referring now to FIG. 12A, on phase P3 of the 3-phase clock,all of the switches S28-S33 are in the open condition. The capacitor C1is charged to V_(ref) in response to the logic state 1 on terminal 172.Capacitors C2, C3 and C4 are all discharged to ground in response to thelogic state 0 signals on terminals 178, 184, 190, respectively.Referring now to FIG. 12B, on phase P1 of the 3-phase clock, all of thecharging switches S3, S6, S9 and S12 (FIG. 5) and the switches S32, S33are in an open condition, and all of the charge sharing switches S28-S31are in a closed condition, wherein the charge on capacitor C1 (FIG. 5)of the one-bit DAC 162 is redistributed, whereby capacitor C1 retains ½of the charge and capacitor C2 (FIG. 5) of one-bit DAC 164 receives ½ ofthe charge. In the event that either capacitor C3 or capacitor C4 hadcharge, the charge would be redistributed between capacitor C3 andcapacitor C4. Referring now to FIG. 12C, on phase P2 of the 3-phaseclock charge sharing switches S29 and S31 are in the open condition,switches S32 and S33 are in the closed condition, and capacitors C1 ofone-bit DAC 162 (FIG. 5) and C3 of one-bit DAC 166 (FIG. 5) deliverstheir charge to the output terminal 160. On the next phase P3 (notshown), the multi-bit digital signal bit₁, bit₂, bit₃, and bit₄ may beupdated and provided to the DAC 150 via input terminals 172, 178, 184,190.

FIG. 13 is a schematic diagram of another embodiment of the SC DAC 150,which receives the 4-bit digital signal, bit₁, bit₂, bit₃, bit₄, oninput terminals 172, 178, 184, and 190, respectively, and outputs ananalog signal on output terminal 160 indicative of a sum of the valuesof the bits in the 4-bit digital signal. In this embodiment, the SC DAC150 comprises four one-bit DACs 202, 204, 206, 208 which are similar tothe one-bit DACs 162, 164, 166, 168 (FIG. 5) except that the one-bitDACs 202, 204, 206, 208 each have an additional path 212, 214, 216, 218,respectively, that connects to the respective capacitor C1, C2, C3, C4.The first terminal of the capacitor C1 connects to a first terminal of acharge sharing switch S43, a second terminal of which connects to thefirst terminal of the capacitor C2. The first terminal of the capacitorC2 further connects to a first terminal of a charge sharing switch S44,a second terminal of which connects to the first terminal of thecapacitor C3 which is further connected to a first terminal of a chargesharing switch S45. A second terminal of the charge sharing switch S45is connected to the first terminal of the capacitor C4 which furtherconnects to a first terminal of a charge sharing switch S46. A secondterminal of the charge sharing switch S46 connects to the first terminalof the capacitor C1. The first terminal of the capacitor C3 is furtherconnected to a first terminal of an output switch S47, a second terminalof which connects to the output terminal 160.

FIGS. 14A-14C are block diagrams showing the operation the SC DAC 150 ofFIG. 13 if input terminals 172, 178, 184, and 190 are supplied withdigital bit signals bit₁, bit₂, bit₃, bit₄, having logic states of 1, 0,0, 0, respectively. Tables show the relationship between the clock phaseand the state (i.e., voltage and charge) of the capacitors in theone-bit DACs. Referring now to FIG. 14A, on phase P3 of the 3-phaseclock, all of the charge sharing switches S43, S44, S45, and S46 and theoutput switch S47, are in the open condition. The capacitor C1 ischarged to V_(ref) in response to the logic 1 on terminal 172.Capacitors C2, C3 and C4 are all discharged to ground in response to thelogic 0 signals on terminals 178, 184, 190, respectively. Referring nowto FIG. 14B, on phase P1 of the 3-phase clock all of the chargingswitches S3, S6, S9 and S12 (FIG. 13) and the output switch S47 are inan open condition, and all of the charge sharing switches S43, S44, S45and S46 are in a closed condition, whereby charge is redistributed andresults in the total charge on all of the capacitors being divided amongall of the capacitors. Because the capacitors C1, C2, C3, C4 all havethe same capacitance value, the charge is shared equally so that thevoltage across each capacitor becomes V_(ref)/4. Referring now to FIG.14C, on phase P2 charge sharing switches S43, S44, S45, and S46 are inthe open condition, output switch S47 is in the closed condition, andcapacitor C1 (FIG. 5) of one-bit DAC 202 delivers its charge to theoutput terminal 160. On the next phase P3 (not shown), the multi-bitdigital signal bit₁, bit₂, bit₃, and bit₄ may be updated and provided tothe DAC 150 via input terminals 172, 178, 184, 190.

Other embodiments have further DAC and switch arrangements andconfigurations. For example, in one embodiment, the DAC includes one-bitDACs that are substantially identical to one another, and interconnectedthrough the switch network to form an “open arrangement”, suchembodiment being referred to herein as a “snake arrangement”.

FIG. 15 is a block diagram of another embodiment of the SC DAC 150,which is similar to the SC DAC 150 illustrated in FIGS. 9, 10A-10C,except that the SC DAC 150 of FIG. 15 further comprises a switch S48, aswitch S49, and a switch S50. A first terminal of the switch S48 isconnected to the second terminal of the charge sharing switch S43. Afirst terminal of the switch S49 is connected to the second terminal ofthe charge sharing switch S45. A first terminal of the switch S50 isconnected to the second terminal of the charge sharing switch S46. Eachof the switches S48, S49, and S50 may, but need not serve one or more ofthe functions noted hereinbelow. In one embodiment, one purpose of theswitches S48, S49, S50 is to provide parasitic capacitance similar tothat of output switch S47, so as to help cancel the effect of theparasitic capacitance of switch S47.

FIG. 16A shows a schematic diagram of another embodiment of a one-bitDAC 221, that includes the one-bit DAC 204, the switch S43 and theswitch S48 of the SC DAC 150 of FIG. 15. The one-bit DAC 204 includes aswitched capacitor (SC) portion 220 and a switch control portion 222.The SC portion 220 includes the switch S4, the switch S5, and thecapacitor C2. The switch control portion 222 has an AND gate 223A thatreceives the phase signal P3 and the digital signal bit₂ and outputs asignal, on signal line 223B, that is used to control the switch S4. Thedigital signal bit₂ is further provided to the inverter 180, whichoutputs a signal 182 that is supplied to an AND gate 223C that furtherreceives the phase signal P3 and outputs a signal, on signal line 223D,that is used to control the switch S5.

FIG. 16B shows a schematic diagram representative of one embodiment of alayout of a switched capacitor cell (SC cell) 300, which may be used forexample in forming a SC DAC. In this embodiment, the SC cell 300comprises the SC portion 220 (FIG. 16A) of the one-bit DAC 204 (16A)including the switch S4, the switch S5, and the capacitor C2. The SCcell 300 further includes switch S43, switch S48, and conductors toprovide control signals to the switches of the SC cell 300. For example,SC cell 300 includes a conductor with a terminal 302 to provide acontrol signal to switch S48, a conductor with a terminal 304 to providea control signal to switch S43, a conductor with a terminal 306 toprovide a control signal to switch S4, and a conductor with a terminal308 to provide a control signal to switch S5. The SC cell furtherincludes a conductor with a terminal 310 to connect to a terminal of theswitch S43, a conductor with a terminal 311 to connect to a terminal ofthe switch S48, and further includes a conductor with a set of terminals312, 314 to connect to the capacitor C2. The terminals 302, 304, 306,308, 310, 311, 312, 314, are disposed along the perimeter of the SC cell300. The SC cell has a reference direction D₃₀₀.

In this embodiment, the footprint of each SC cell is square or at leastsubstantially square. In another example embodiment, the footprint maybe octagonal or at least substantially octagonal. In one embodiment,switch terminal 310 has substantially identical composition and surfacearea as switch terminal 311, and contributes the same amount ofcapacitance as switch terminal 311. In one embodiment, the capacitor isdisposed such that the center of the capacitor coincides with, or atleast substantially overlays, the center of the footprint of the SCcell.

Referring now to FIG. 16C, an SC cell 300A is schematically identical tothe SC cell 300. The SC cell 300A has a reference direction D_(300A).The SC cell 300 is adapted to electrically connect to the SC cell 300Aif the SC cell 300A is positioned adjacent to the SC cell 300 andoriented such that its reference direction D_(300A) is directed in thesame direction as the reference direction D₃₀₀ of the SC cell 300. Insuch position and orientation, the terminal 314 on SC cell 300electrically connects to the terminal 310A on SC cell 300A, therebycoupling capacitor C2 of SC cell 300 to capacitor C2A of SC cell 300Athrough switch S43A.

Referring now to FIG. 16D, in some embodiments, the SC cell 300 isfurther adapted to electrically connect to the SC cell 300A if the SCcell 300A is positioned adjacent to the SC cell 300 and oriented suchthat its reference direction is directed in a direction having apredetermined angular offset from the reference direction D₃₀₀ of the SCcell 300. In this embodiment, the predetermined angular offset is ninetydegrees. In other embodiments, other predetermined angular offsets maybe employed. In such position and orientation, the terminal 312 on SCcell 300 electrically connects to the terminal 311A on SC cell 300A,thereby coupling capacitor C2 of SC cell 300 to capacitor C2A of SC cell300A through switch S48A.

FIG. 16E shows four identical SC cells, i.e., an SC cell 300, an SC cell300A, an SC cell 300B, and a SC cell 300C. The SC cell 300 has areference direction D₃₀₀. The SC cell 300A has a reference directionD_(300A). The SC cell 300B has a reference direction D_(300B). The SCcell 300C has a reference direction D_(300C). The SC cell 300A isoriented such that its reference direction D_(300A) is directed in adirection offset ninety degrees from the reference direction D₃₀₀. TheSC cell 300B is oriented such that its reference direction D_(300B) isdirected in a direction offset ninety degrees from the referencedirection D_(300A). The fourth SC cell 300C is oriented such that itsreference direction D_(300C) is directed in a direction offset ninetydegrees from the reference direction D_(300B). Such embodiment is onetype of a “ring arrangement”. If the SC cells 300, 300A, 300B, 300C arepositioned adjacent to one another and oriented as shown, then each ofthe SC cells has a switch terminal 311 connected to a capacitor terminal312 of a neighboring SC cell, and further has a capacitor terminal 312connected to a switch terminal 311 of a neighboring cell.

FIG. 17 shows one embodiment of the SC DAC 150 that is formed, at leastin part, by SC cells arranged into a “ring arrangement”. In thisembodiment, the SC DAC 150 includes four one-bit DACs 202, 204, 206,208. The one-bit DAC 202 includes an SC cell 300A and a switch controlportion 350. The one-bit DAC 204 includes an SC cell 300B and a switchcontrol portion 352. The one-bit DAC 206 includes an SC cell 300C and aswitch control portion 354. The one-bit DAC 208 includes the SC cell300D and a switch control portion 356. The SC cell 300A has a referencedirection D_(300A). The SC cell 300B has a reference direction D_(300B).The SC cell 300C has a reference direction D_(300C). The SC cell 300Dhas a reference direction D_(300D). The reference direction D_(300B) isdirected in a direction that is offset ninety degrees from the referencedirection D_(300A). The reference direction D_(300C) is directed in adirection that is offset ninety degrees from the reference directionD_(300B), The reference direction D_(300D) is directed in a directionthat is offset ninety degrees from the reference direction D_(300C).

The digital signal bit₁ and the phase P3 signal are supplied to theswitch control portion 350, which generates switch control signals, onsignal lines 360, 362 supplied to the SC cell 300A. The digital signalbit₂ and the phase P3 signal are supplied to the switch control portion352, which generates switch control signals, on signal lines 364, 366supplied to the SC cell 300B. The digital signal bit₃ and the phase P3signal are supplied to the switch control portion 354, which generatesswitch control signals on signal lines 368, 370 supplied to the SC cell300C. The digital signal bit₄ and the phase P3 signal are supplied tothe switch control portion 356, which generates switch control signals,on signal lines 372, 376 supplied to the SC cell 300D.

FIG. 18 shows an embodiment of the SC DAC 108 (FIG. 3) that is adaptedto convert a two bit binary-weighted input signal bit₁, bit₂ into acorresponding analog signal. This embodiment of a switched capacitor DACis disclosed in F-J. Wang et al., “A Quasi-Passive CMOS Pipeline D/Aconverter”, IEEE Journal of Solid State Circuits, Vol. 24, no. 6,December 1989, pp. 1752-1755. In this embodiment of the SC DAC 108, thevalues of C101, C102, C103 are substantially identical. The SC DAC 108receives a non-overlapping 3-phase clock, P1, P2, P3, e.g., shown inFIG. 3. The closed/open condition of the switches S102, S103, S104,S105, S106, S109 is controlled by the 3-phase clock. The closed/opencondition of the switches S100, S101, and the switches S107, S108 arecontrolled by the logic state of the LSB and the MSB, respectively.

FIGS. 19A-19C are block diagrams showing the operation of the SC DAC 108of FIG. 18 for each of the 3 clock phases in the event that the LSB andthe MSB digital input signals have logic states of 1, 0, respectively.Tables show the relationship between the clock phase, and the state(i.e., voltage and charge) of the capacitors in the one-bit DACs.Referring now to FIG. 19A, on phase P1 of the 3-phase clock, switch S102and switch S104 are in the closed condition whereby capacitor C102 isdischarged to ground, and capacitor C101 is charged to V_(ref) inresponse to the state of the LSB. Referring now to FIG. 19B, on phase P2switches S102 and S104 are in the open condition. Switch S103 is in theclosed condition whereby C101 and C102 split the charge initially storedon C101. Because the capacitors C101 and C102 have the substantially thesame capacitance value, the charge is shared equally so that the voltageacross each capacitor becomes V_(ref)/2. Referring now to FIG. 19C, onP3 of the 3-phase clock charge sharing switch S105 is in the closedcondition, S102-S104, S106, and S109 are in the open condition. C101 andC103 share charge, in specific, C101 and C103 split the charge fromC101. Because the capacitors C101 and C102 have substantially the samecapacitance value, the charge is shared equally so that the voltageacross each capacitor becomes V_(ref)/4. On the next phase P1 (see FIG.19A for switch configuration), output switch S109 is in the closedcondition, and capacitor C103 delivers its charge to the output.

FIG. 20 is a block diagram of another of the DAC portion 110 of the DACstage 86 shown in FIG. 3. In this embodiment, an output terminal 111 ofthe SC DAC 108 for processing the MSB of the binary-weighted multi-bitdigital input signal is coupled to one of the charge sharing switches ofthe segmented SC DAC 114 (FIG. 3).

FIG. 21 is a schematic representation of one embodiment of the DACportion 110 shown in FIG. 20. In this embodiment, the DAC portion 110includes an SC DAC 150 such as that described above with respect to FIG.17. The DAC portion 110 further includes an SC DAC 108 (only MSB portionshown), such as that described above with respect to FIG. 18. A one-bitDAC for processing the MSB includes a SC cell 380 and a switch controlportion 382. The digital signal MSB and the phase P2 signal are suppliedto the switch control portion 382, which generates switch controlsignals on lines 384, 386, that are supplied to the SC cell 380. Anoutput terminal of the SC cell 380 is coupled to one of the SC cells300A, 300B, 300C, 300D, e.g., SC cell 300D.

In this embodiment, the SC DAC 108 and the SC DAC 150 each receive anon-overlapping three phase clock. On phase P2, the one-bit DAC of theMSB of the SC DAC 108 undergoes pre-charge in accordance with the logicstate of the MSB signal into the SC DAC 108. On phase P3, a chargesharing switch of the SC DAC 108 is in the closed condition, whereby theone-bit DAC of the MSB portion of the SC DAC 108 shares charge with thepreceding one-bit DAC of the SC DAC 108. Also on phase P3, the SC DAC150 undergoes pre-charge in accordance with the multi-bit digitalsignal, bit₁, bit₂, bit₃, bit₄. On phase P1, the charge sharing switchesof the SC DAC 150 are in the closed condition, whereby charge isredistributed among the one-bit DACs in the SC DAC 150 and the one-bitDAC of the MSB of the SC DAC 108. On phase P2, switch S48 is in theclosed condition, and one of the one-bit DACs of the SC DAC 150 deliverscharge, i.e., a data sample, to the output terminal 120 of the DACportion 110 of the DAC stage 86 (FIG. 3).

FIG. 22 is a schematic representation of another embodiment of the DACportion 110 shown in FIG. 20. In this embodiment, the SC DAC 150includes 3 one-bit DACS, 202, 204, 206. In this embodiment, unlike theembodiment of FIG. 21, the MSB portion of the SC DAC 108 is positionedin the “ring arrangement” of the SC DAC 150. Thus, besides the SC cell380 used for the MSB portion of the SC DAC 108 (FIG. 3) there are threeother SC cells in the ring arrangement. Operation of the DAC portion 110shown in FIG. 22 is similar to that described above with respect to theDAC portion 110 of FIG. 21.

FIG. 23 is a block diagram of another embodiment of the DAC stage 86,which receives a binary-weighted multi-bit digital signal on signallines 82. The binary-weighted multi-bit digital signal is divided into abinary-weighted LSB portion and a binary-weighted MSB portion. The LSB'sare supplied to a switched capacitor (SC) DAC 108 that forms an analogsignal corresponding to the value represented by the LSB's. The MSB'sare supplied to a thermometer encoder 112 that converts the MSB's intoan equally-weighted multi-bit digital signal. The equally-weightedmulti-bit digital signal is input to a scrambler 400, and help reducethe effects of the noise and/or distortion produced by the digital toanalog converter. The scrambler 400 outputs equally-weighted scrambledbits which are supplied to a switched capacitor (SC) DAC 114. The SC DAC114 forms an analog signal corresponding to the value represented by theequally-weighted, scrambled, multi-bit digital signal. The analog signalfrom the SC DAC 108 and the analog signal from the segmented SC DAC 114are summed at 118 to form an analog signal, output on signal line 120.

FIG. 24 is a block diagram of one embodiment of a four-bit scrambler 400that receives a three-bit digital input signal, bit_(A), bit_(B),bit_(C), represented by the labeled arrows on the left, and outputsscrambled bits, represented by the arrows on the right. A scrambler istypically most effective when all of the scrambler inputs receive data.The extra input(s) of the scrambler may for example be “hardwired” to alogic state, i.e., a 1 or a 0. In this event that an input(s) of ascrambler is hardwired, it may be desirable to hardwire a correspondingnumber of DAC input(s), to a logic state opposite to that used for theextra input(s) of the scrambler.

The scrambler may be any type of scrambler. For example, variousscramblers and scrambler configurations are disclosed in U.S. Pat. Nos.5,977,899 and 5,404,142, and in Kwan, Tom, et al., “A Stereo MultibitSigma-Delta DAC with Asynchronous Master-Clock Interface”, IEEE Journalof Solid-State Circuits, Vol. 31, No. 12, December 1996, pp. 1881-1887.In addition, the scrambler may use any of various schemes, e.g., datadirected, random swapping.

FIG. 25 is a schematic representation of one embodiment of the DACportion 110 of the DAC stage 86 shown in FIG. 20. In this embodiment,unlike the embodiment of FIG. 22, the MSB portion of the SC DAC 108 isone of six SC cells in a “ring arrangement”. Thus, besides the SC cell380 used for the MSB portion of the SC DAC 108 (FIG. 3) there are fiveother SC cells in the ring arrangement, namely, SC cells 300A-300E. Inthis embodiment, the five SC cells 300A-300E form a segmented SC DAC 114(FIG. 3). SC cell 380 and SC cell 300D are similarly oriented to eachother, i.e., D380 and D300 _(D) are directed in similar direction toeach other. Likewise, SC cell 300B and SC cell 300E are similarlyoriented to each other.

The bits bit₁, bit₂, bit₃, bit₄, of the multi-bit digital signal aresupplied to the SC cells 300A, 300B, 300C, 300D, respectively. The SCcell 300E may be supplied with a signal having a “hardwired” logicstate. In some embodiments, supplying such an input signal has an effecton the “gain” of the SC DAC 114 (FIG. 3). Some embodiments may providecompensation for any “gain” effect. Compensation may for example beprovided in the digital signal processor stage 109 (FIG. 3), the signalconditioning stage 89 (FIG. 3), or in the DAC portion 10 (FIG. 3), orany combination thereof In addition, the input signal may be of a typethat does not result in a “gain” effect”. If an input signal is suppliedto the SC cell 300E, the signal is not limited to one hardwired to alogic state but rather may be any type of signal, and may be timevarying or non-time varying.

FIG. 26 is a schematic block diagram of another embodiment of the DACstage 86 (FIG. 3). An MSB portion of an equally-weighted multi-bitdigital signal is input to the scrambler 400, which outputsequally-weighted scrambled bits to a gating stage 420. The gating stage420 (sixteen gating stages) further receives one of the clock phasesignals, e.g., P3, and outputs gated, equally-weighted scrambled bits toa switched capacitor (SC) DAC 114. The SC DAC 114 forms an analog signalcorresponding to the value represented by the equally-weighted,scrambled, multi-bit digital signal. The analog signal from the SC DAC108 is supplied to the segmented SC DAC 114, which form an analogsignal, on signal line 120, corresponding to the value represented bythe multi-bit digital signal input to the DAC stage 86. Scrambler 400further receives an input signal for example having a logic state of 1.An additional gating stage 421 receives an input signal for examplehaving a logic state of 0. Thus there are seventeen gating stages intotal.

In one embodiment, the DAC stage 86 (FIG. 3) operates at a cycle ratelower than that of the SC filter stage 90, for example, the DAC stage 86(FIG. 3) may operate at a cycle rate of 6.5 MHz and the SC filter mayoperate at a cycle rate of 13 MHz.

Digital-to-analog conversion often results in noise, e.g., quantizationnoise, and/or distortion, caused for example, by non-linearities, e.g.,integral and/or differential, within the digital-to-analog converter,which in turn is caused by, among other things, mismatching of analogcomponents within the digital-to-analog converter. As stated above,signals from the digital to analog converter may be supplied to a signalconditioning stage that may comprise an analog filter, for example, aswitched capacitor (SC) filter stage. The signal conditioning stage mayhelp attenuate noise and/or distortion components of the analog signals,for example, by removing out of band noise. However, a reduction in anyparticular noise and/or distortion need not be sought nor obtained inevery embodiment, and is not a requirement of the signal conditioningstage or the switched capacitor techniques disclosed herein.

FIG. 27 is a schematic diagram of one embodiment of a portion of the DACstage 86 in combination with one embodiment of the SC filter stage 90.In this embodiment, the DAC stage 86 and the SC filter stage 90 eachreceive a non overlapping four phase clock. However, the cycle rate ofthe DAC stage, is less, e.g., about 50% less than the cycle rate of theSC filter stage 90. In this embodiment, the output of the SC DAC is inthe form of charge packets, which are provided to the switched-capacitorfilter as described below. Data may be pipelined through thedigital-to-analog converter and into the switched capacitor filter,wherein the output data rate of the digital-to-analog converter ismatched to the input data rate requirements of the switched capacitorfilter.

The output of the input op amp is valid on phase P3 and on phase P1. Onphase P3, the one-bit DAC 202 and one-bit DAC 204 pre-charge in responseto the logic state of bit₁ and bit₂, respectively, as described abovewith respect to FIG. 13. DAC stage switches S59, S60, S61, and S62 arein the open condition. Also on phase P3, SC filter stage switches S63,S64, S68, S69, S72, and S74 are in the open condition. Switches S65,S66, S67, S70, S71, and S73 are in the open condition. On phase P4, thecharge sharing switches, e.g. S59 and S60 of the SC DAC stage are in theclosed condition, whereby charge is redistributed among the one-bitDACs. Also on phase P4, SC filter switches S63, S64, S68, S69, S72, andS74 are in the closed condition. Switches S65, S66, S67, S70, S71, andS73 are in the open condition, whereby the input op amp of the SC filterstage 90 undergoes offset and gain compensation. Gain compensation ismost effective when the sample rate is much higher than the bandwidth ofthe analog signals from the DAC stage. On phase P1, switch S61 closesand one of the one-bit DACs of the SC DAC delivers charge, i.e. a datasample, to input of the SC filter stage, which in this embodimentappears as a offset and gain compensated virtual ground. Switches S59and S60 are in the open condition. Also on P1, the SC filter stage 90switches S67 and S70 are in the closed condition, through which theoutput of the SC filter stage 90 is connected back to the input of theSC filter stage 90. Switches S65, S71, and S73 are in the closedcondition as well. Switches S63, S64, S68, S69, S72, and S74 are in theopen condition. On phase P2, SC filter switches S62 and S63 are in theopen condition thereby opening the connection between the output and theinput of the SC filter stage 90. Switch S62 is in the closed conditionwhereby the one-bit DAC 202 delivers charge, i.e. a data sample, toinput of the SC filter stage. Switches S61, S60, and S59 are in the opencondition. Also on phase P2, switch S65, S66, S68, S69, S72, and S74 arein the closed condition. Switches S63, S64, S67, S70, S71, S73 are inthe open condition. On phase P3, switches S59, S60, S61, and S62 are inthe open condition and the SC DAC undergoes another precharge inaccordance with the multi-bit input signal.

Thus, the DAC stage delivers more than one analog signal (e.g., twoanalog signals in this embodiment), during each cycle of the DAC (e.g.,each cycle of the four phase clock), whereby the output sample rate ofthe DAC matches the input sample rate of the SC filter stage. The analogsignals may but need not be identical to one another. In someembodiments, the two analog signals from the DAC are not identical butthe downstream stages provide appropriate compensation so that the twoanalog signals contribute equally to the output of the Digital to AnalogConversion System. Any type of SC DAC may be used so long as the DACgenerates suitable “copies” of the analog signal. In some embodiments, aSC DAC of the type shown in FIGS. 18 and 19A-19C may be used because itcan inherently provide multiple copies of the output signal.

The signal conditioner stage need not be a switched capacitor filter.Thus, although described above as including a SC filter stage, someembodiments may not include a an SC filter stage. Furthermore, inembodiments having a SC filter stage, offset and gain compensation isnot required.

There are many ways to physically arrange the stages in each of thefigures. For example, in one embodiment, one gate stage is integratedinto each of the SC cells in order to reduce the number of data linesthat are routed to the DAC stage. In another embodiment, the gate stagesare integrated near the scrambler cell in order to reduce the size ofthe SC cells.

In some embodiments, the value of the capacitance used in the SC DAC maybe selected in accordance with kT/C noise requirements, although this isnot required.

In some embodiments, the value of the capacitance used in the SC DAC maybe selected so as to be large enough to meet bit weight matchingrequirements. However, these are just two example criteria. The criteriafor selecting the value(s) of the capacitance used in the SC DAC are notlimited to those of noise requirements and/or bit weight matchingrequirements.

Although described with respect to a system for use in a GSM system thatruns at 13 MHz, the systems described above are not limited to such.

Various switched capacitor filters and associated configurations aredisclosed in Temes, Gabor C., et al. “Novel Pipeline Data Converters”,ISCAS, 1988, pp. 1943-1946, and Yoshizawa, Hirokazu, et al., “NovelDesign Techniques for High-Linearity MOSFET-Only Switched-CapacitorCircuits”, Symposium on VLSI Circuits Digest of Technical Papers, 1996,pp. 152-153.

In some embodiments, the DAC stage simultaneously delivers multiple“copies” at the same time, which in effect increases the gain of theDAC.

Referring again to FIG. 27, in some embodiments the SC filter stage 90has a switched capacitor, e.g., C400. The switched capacitor C400 may bebut is not limited to a switched capacitor that does not have effectsfrom associated parasitic capacitances. In other words, the parasiticcapacitances may or may not be charged and/or discharged and do not passparasitic signals from the charging and discharging events into thesignal path. In this embodiment, the SC filter stage includes a switchedcapacitor C401 in parallel with the switched capacitor C400. Switchedcapacitor C400 may or may not share switches with the switched capacitorC401. The switched capacitor C401 may exhibit parasitic capacitancecharacteristics. The switched capacitor C401 may be for example, but isnot limited to a switched capacitor formed of two diodes that areconnected anode to anode or are connected cathode to cathode, where thejunction between the two diodes is biased such that the diodes do notbecome forward biased during operation. In some embodiments, the DACstage has parasitic sensitive switched capacitor elements andconsequently the capacitor C401 in the switched capacitor filter mayimprove gain matching and/or gain drift between the DAC stage and the SCfilter stage.

FIG. 28A is an illustration of a top view of one embodiment of a SC cell450 implementing the one-bit DAC of FIG. 16A. The perimeter of the SCcell 450 is shown as a dotted line. The SC cell 450 includes a capacitortop plate C1TP and a capacitor bottom plate C1BP. A conductor 452 isprovided to supply the digital signal bit₂ to a region of a controlportion 222. A conductor 454 is provided to supply the phase signal P3to a region representing a control portion 222. A conductor 456 runsfrom the perimeter of the SC cell 450 to a gate of a switch S43. Aconductor 458 runs from the perimeter of the SC cell 450 to one of asource or a drain of the switch S43. A conductor 460 runs from theperimeter of the SC cell 450 to the top plate of the capacitor C1TP andto the other of the source or drain of the switch S43. A conductor 462runs from the perimeter to one of a source or a drain of a switch S48. Aconductor 464 runs from the other of the source or drain of the switchS48 to the top plate of the capacitor C1TP and to a region 466representing a region of a switch S4, a switch S5, voltage reference V3,and voltage reference V4. A conductor 468 runs from a gate of the switchS48 to the perimeter of the SC cell 450.

FIG. 28B is an illustration of a top view of another embodiment of a SCcell 450 implementing the one-bit DAC of FIG. 16A. This embodiment issubstantially the same as the embodiment of FIG. 28A but furtherincludes a switch S43A that is electrically in parallel with S43 andphysically oriented substantially perpendicular to S43; and furtherincludes a switch S48A that is electrically in parallel with S48 andphysically oriented perpendicular to S48. For example, the switches S43,S43A may have a longitudinal axis, and the switches may be oriented suchthat the longitudinal axis of one switch is physically perpendicular tothe longitudinal axis of the other switch. In one embodiment, theswitches S43 and S43A are formed of two switches of approximately equalsize.

FIG. 29 is a representation of a top view of one embodiment of a dielayout 480 of a DAC portion 110 having eighteen SC cells arranged in aring 482. Seventeen of the SC cells (shown in solid lines) in the ringform a segmented DAC adapted to receive a multi-bit digital input signalhaving up to seventeen bits. One of the SC cells (shown in dotted line)in the ring forms the MSB portion of a SC DAC (shown in dotted line) 484formed of seven SC cells and adapted to receive a multi-bit digitalinput signal of up to seven bits. An arrow on each of the SC cells inthe ring indicates the relative direction of orientation of the SC cell.

In one embodiment, the DAC stage is fabricated in a 0.25 micron (μ)double-poly quad metal process in a GSM baseband/voiceband integratedcircuit.

However, as stated above, the switches and the capacitors are notlimited to the particular embodiments shown.

As stated above, switched capacitor techniques are used in many systems.Thus, the switched capacitor devices and techniques described above arenot limited to mobile communication systems or even digital to analogconverters.

FIG. 30 is a schematic diagram of one embodiment of the CT filter stage92 of FIG. 2, which includes a two resistors R600, R601 that eachreceive an analog signal from the SC filter stage, and form an RC filterwith C600 and C601, to passively filter the images left by the switchedcapacitor filter. The images appear at multiples of the SC filter samplerate. The stage may have selectable gain formed by an amplifier 600 andresistors R602-R607. The CT filter stage may further provide resistorsR608, R609, which form a passive pole in combination with an off-chipcapacitor C602. Although not required, the resistors in the output polemay be integrated to improve I/Q channel matching, reduce externalcomponent count and to reduce the effects of loading from the pincapacitance on the output stage amplifier.

FIG. 31 is a block diagram of one embodiment of a squaring circuit 500that is adapted to convert a 4-bit digital input signal bit₁, bit₂,bit₃, bit₄, into an analog signal indicative of the square of the inputsignal. The analog signal is supplied to an output terminal 510. Thesquaring circuit 500 comprises four switched capacitor DACs 162, 164,166, 168, described above with respect to FIG. 5. The digital signalbit₁ is presented to an input terminal 512 from where it is supplied tothe one-bit DAC 162 to control the switch S1. The digital signal bit₁ isfurther supplied to an inverter 174 that generates a signal at terminal176 used to control switch S2. The digital signal bit₂ is presented toan input terminal 514 from where it is supplied to the one-bit DAC 164to control switch S4 and input to an inverter 180 that generates asignal at terminal 182 used to control switch S5. The digital signalbit₃ is presented to an input terminal 516 from where it is supplied tothe one-bit DAC 166 to control switch S7 and input to an inverter 186that generates a signal at terminal 188 used to control switch S8. Thedigital signal bit₄ is presented to an input terminal 518 from where itis supplied to the one-bit DAC 168 where it is used to control chargingswitch S10 and input to an inverter 192 that generates a signal atterminal 194 used to control switch S11. The first terminal of thecapacitor C1 is supplied to a first terminal of a charge sharing switchS200. The first terminal of the capacitor C2 is supplied to a firstterminal of a charge sharing switch S201. The first terminal of thecapacitor C3 is supplied to a first terminal of a charge sharing switchS202. The first terminal of the capacitor C4 is supplied to a firstterminal of a charge sharing switch S203. The second terminal of each ofthe switches S200-203 is connected to a first terminal of a switch S204.The second terminal of the switch S204 is connected to the outputterminal 510.

FIGS. 33A-33C are block diagrams showing the operation of the squaringcircuit 500 of FIG. 31 for each of the three clock phases in the eventthat input terminals 512, 514, 516, 518 are supplied with digital bitsignals bit₁, bit₂, bit₃, bit₄, having logic states of 1, 0, 0, 0,respectively. Tables show the relationship between the clock phase, andthe state (i.e., voltage and charge) of the capacitors in the one-bitDACS. Referring now to FIG. 33A, on phase P3 of the 3-phase clock, allof the charge sharing switches S200, S201, S202, and S203 and the outputswitch S204, are in the open condition. The capacitor C1 is charged toV_(ref) in response to the logic state 1 on terminal 512. Capacitors C2,C3 and C4 are all discharged to ground in response to the logic state 0signals on terminals 514,516,518, respectively. Referring now to FIG.33B, on phase P1 of the 3-phase all of the charging switches S3, S6, S9and S12 (FIG. 31) and the output switch S204 are in an open condition,and all of the charge sharing switches S200, 201, 202, 203 are in aclosed condition, whereby charge is redistributed and resulting in thetotal charge on all of the capacitors being divided among all of thecapacitors. If the capacitors C1, C2, C3, C4 all have the samecapacitance value C, then the charge is shared equally so that thevoltage across each capacitor becomes V_(ref)/4. Referring now to FIG.33C, on P2 of the 3-phase clock switch S200 is in the closed conditionbecause P2 has a logic 1 state and bit₁ has a logic state 1. SwitchesS201, S202, S203 are in the open condition because bit₂, bit₃, bit₄,have a logic state 0. Output switch S204 is in the closed condition, andcapacitor C1 (FIG. 31) of one-bit DAC 162 delivers its charge to theoutput terminal 510. Consequently, the total charge delivered to theoutput terminal 510 is equal to C*Vref/4.

FIGS. 34A-34C are block diagrams showing the operation of the squaringcircuit 500 of FIG. 31 for each of the 3 clock phases in the event thatinput terminals 512, 514, 516, 518 are supplied with digital bit signalsbit₁, bit₂, bit₃, bit₄, having logic states of 1, 1, 0, 0, respectively.Tables show the relationship between the clock phase, and the state(i.e., voltage and charge) of the capacitors in the one-bit DACs.Referring now to FIG. 33A, on phase P3 of the 3-phase clock, all of thecharge sharing switches S200, S201, S202, and S203 and the output switchS204, are in the open condition. The capacitor C1 and the capacitor C2are each charged to V_(ref) in response to the logic state 1 on terminal512 and 514, respectively. Capacitors C3 and C4 are all discharged toground in response to the logic 0 signals on terminals 516, 518,respectively. Referring now to FIG. 34B, on phase P1, all of thecharging switches S3, S6, S9 and S12 (FIG. 31) and the output switchS204 are in an open condition, and all of the charge sharing switchesS200, 201, 202, 203 are in a closed condition, whereby charge isredistributed and resulting in the total charge on all of the capacitorsbeing divided among all of the capacitors. If the capacitors C1, C2, C3,C4 all have the same capacitance value C, then the charge is sharedequally so that the voltage across each capacitor becomes V_(ref)/2.Referring now to FIG. 33C, on P2 of the 3-phase clock, switch S200 is inthe closed condition because P2 has a logic state 1 and bit₁ has a logicstate 1. Switch S201 is in the closed condition because P2 has a logicstate 1 and bit₂ has a logic state 1. Switches S202, S203 are in theopen condition because bit₃, bit₄, have a logic state 0. Output switchS204 is in the closed condition, and capacitors C1 and C2 (FIG. 31) ofone-bit DACs 162, 164 delivers charge to the output terminal 510.Consequently, the total charge delivered to the output terminal 510 isequal to C*Vref.

Thus, for this embodiment, the charge may be determined as follows:Charge=(C*Vref*(value of digital input)^2)/4  (Equation 1)

In other embodiments, the multi-bit digital input signal to the SCsquaring circuit need not be equally-weighted bits, but rather may havebinary-weighting or any other weighting.

FIG. 35 shows one embodiment of an analog to digital converter 800. Theanalog to digital converter 800 is a successive approximation typehaving an analog comparison stage 801 that receives an analog signal.The analog comparison stage 801 generates an output signal that issupplied to a successive approximation register (SAR), which generatesan output signal that is supplied to a latch stage 804. A digital outputsignal from the latch stage 804 is fed back to an input of the analogcomparison stage through a feedback element 806. The feedback element806 may be a digital to analog converter that employs one or more of themethods or devices described hereinabove. In some embodiments, thefeedback element may comprise a squaring circuit such as for example,the squaring circuit described hereinabove with respect to FIGS. 31-34.In such embodiments, the feedback DAC has the characteristic that theanalog output is proportional to the square of the digital input. Thisproduces a square root transfer function for the overall analog todigital converter, wherein the digital output is proportional to thesquare root of the analog input. In contrast, the AD574 analog todigital converter, manufactured by Analog Devices, Inc. produces alinear transfer function, wherein the digital output is directlyproportionate to the analog input of the analog to digital converter.

Referring again to FIG. 31, in another embodiment, a digital to analogconverter may receive a first multi-bit digital signal and a secondmulti-bit digital signal, and generate an analog signal indicative of aproduct of the first multi-bit digital signal and the second multi-bitdigital signal. Such embodiment is similar to the squaring circuit ofFIG. 31 except that the switches S200, S201, S202, and S203 arecontrolled by the second multi-bit digital signal. For example, theswitch S200 may be controlled according to an equation: P1+((bit₁ ofsecond multi-bit digital signal)*P2). The switch S201 may be controlledaccording to an equation: P1+((bit₂ of second multi-bit digitalsignal)*P2). The switch S202 may be controlled according to an equation:P1+((bit₃ of second multi-bit digital signal)*P2). The switch S203 maybe controlled according to an equation: P1+((bit₄ of second multi-bitdigital signal)*P2). In another embodiment, such a digital to analogconverter may be employed in the feedback loop of a analog to digitalconverter, as in FIG. 35.

In another embodiment, the digital signal processing stage includes asigma delta modulator.

Although shown in an embodiment adapted to receive an acoustical signal56, in other embodiments, the handset 50 is not limited to such. Theinput signal may be one or more signal of any type including but notlimited to electromagnetic, electrical, microwave, acoustical,ultrasound, and optical signal, may have any form, and may be from anysource. The invention may be used in any type of system which may butneed not include a digital to analog conversion stage.

The multi-bit digital signal may be parallel data, e.g., provided by wayof plurality of signal lines, serial data, e.g., provided by way of asingle signal line, or any combination thereof, e.g., some parallel dataand some serial data.

Although the SC cell is shown in embodiments for use in forming a SCDAC, the SC cell is not limited to such, but rather may be used in anyapplication.

The switched capacitor devices and techniques described above are notlimited to embodiments in which the elements are substantiallyidentical.

As stated above, the switches and the capacitors may be of any type andare not limited to the particular embodiments disclosed above.

While there have been shown and described various embodiments, it willbe understood by those skilled in the art that various changes andmodifications may be made.

1. A system comprising: a DAC that receives a multi-bit digital signaland outputs at least two analog signals including a first analog signaland a second analog signal, the first analog signal being indicative ofa sum of values of bits in the multi-bit digital signal, the secondanalog signal also being indicative of said sum of values of said bitsin the multi-bit digital signal.
 2. The system of claim 1 wherein thefirst analog signal and the second analog signal are substantially equalto each other.
 3. The system of claim 1 wherein the DAC comprises aswitched capacitor DAC.
 4. A method comprising: receiving a multi-bitdigital signal; and generating at least two analog signals including afirst analog signal that is indicative of a sum of values of bits in themulti-bit digital signal, and a second analog signal that is indicativeof said sum of values of said bits in the multi-bit digital signal. 5.The method of claim 4 wherein the first analog signal and the secondanalog signal are substantially equal to one another.
 6. The method ofclaim 5 wherein generating comprises: charging each of a plurality ofcapacitors to a value corresponding to a value of a bit in the multi-bitsignal; and connecting at least two of the plurality of capacitors toone another to share charge with one another.
 7. The system of claim 1wherein the DAC has a first circuit portion and a second circuitportion, and the first analog output signal is generated based on asignal from the first circuit portion, and the second analog outputsignal is generated based on a signal from the second circuit portion.8. The system of claim 1 wherein the DAC has a first sub DAC and asecond sub DAC, the first analog output signal is generated based on asignal from the first sub DAC, and the second analog output signal isgenerated based on a signal from the second sub DAC.
 9. The system ofclaim 1 wherein the DAC has a plurality of sub DACs that each receive anassociated bit of the multi-bit digital signal, each of the plurality ofsub DACs having an associated capacitance that receives an associatedamount of charge in response to the associated bit, the switchedcapacitor DAC having an operating state in which at least two of theplurality of sub DACs are operatively connected to at times share chargewith one another, effecting a redistribution of charge upon which eachhas a redistributed amount of charge, the first analog output signalbeing generated based on the redistributed charge of one of the subDACs, and the second analog signal being generated based theredistributed charge of another one of the sub DACs.
 10. The system ofclaim 1 wherein the DAC has a first output line and a second output lineand the DAC has at least one operating state in which the first outputline and the second output line are not connected to one another and thefirst analog output signal is output on the first output line, and atleast one operating state in which the first output line and the secondoutput line are not connected to one another and the second analogsignal is output on the second output line.
 11. A system comprising:means for receiving a multi-bit digital signal; and means for generatingat least two analog signals including a first analog signal that isindicative of a sum of values of bits in the multi-bit digital signal,and a second analog signal that is indicative of said sum of values ofsaid bits in the multi-bit digital signal.
 12. The system of claim 11wherein the first analog signal and the second analog signal aresubstantially equal to one another.
 13. The system of claim 11 whereinmeans for generating comprises a switched capacitor DAC.
 14. A systemcomprising: a binary weighted DAC; and a segmented DAC, coupled to thebinary weighted DAC, the segment DAC comprising a switched capacitornetwork that receives a multi-bit digital signal, the switched capacitornetwork having a plurality of sub DACs that each receive an associatedbit of the multi-bit digital signal, each of the plurality of sub DACshaving an associated capacitance that receives an associated amount ofcharge in response to the associated bit, at least two of the pluralityof sub DACs sharing charge with one another, and the switched capacitornetwork outputs at least one analog signal indicative of a sum of valuesof each bit in the multi-bit signal.
 15. A handset for a mobilecommunication system comprising: an input stage that receives an inputsignal and outputs a multi-bit digital signal to a digital-to-analogconversion system that receives the multi-bit digital signal and outputsan analog signal indicative of a sum of values of bits in the multi-bitsignal, and comprising: a switched capacitor network that receives amulti-bit digital signal, the switched capacitor network having aplurality of sub DACs that each receive an associated bit of themulti-bit digital signal, each of the plurality of sub-DACs having anassociated capacitance that receives an associated amount of charge inresponse to the associate bit, wherein the associated amount of chargefor each of the plurality of sub DACs is in direct proportion to aweight of the bit, at least two of the plurality of sub DACs sharingcharge with one another, and the switched capacitor network outputs atleast one analog signal indicative of a sum of values of bits in themulti-bit signal.
 16. A system comprising: a digital signal processingstage that receives a multi-bit input and provides a multi-bit output;and a switched capacitor DAC that receives a multi-bit input signal thatincludes the multi-bit output of the digital signal processing stage,the switched capacitor DAC having a plurality of sub DACs that eachreceive an associated amount of charge in response to the multi-bitinput signal received by the DAC, the switched capacitor DAC having anoperating state in which at least two of the plurality of sub DACs sharecharge with one another such that the associated charges areredistributed, and having an operating state in which the switchedcapacitor DAC outputs an analog signal that is indicative of themulti-bit input signal received by the switched capacitor DAC using lessthan all of the redistributed charge.
 17. The system of claim 16 whereineach of the sub DACs has an associated portion of the redistributedcharge and the at least one analog signal includes an analog signal thatis indicative of and generated in response to the portion of theredistributed charge that is associated with one of the sub DACs. 18.The system of claim 16 wherein the plurality of sub DACs each receive anassociated bit of the multi-bit input signal, and each of sub DACsreceives its associated amount of charge in response to the associatedbit.
 19. The system of claim 16 wherein the associated amount of chargereceived by one of the plurality of sub DACs is equal to zero.
 20. Thesystem of claim 18 wherein the associated bit of one of the plurality ofsub DACs has a low logic state and the associated amount of chargereceived in response to the associated bit is equal to zero.
 21. Thesystem of claim 16 wherein the digital signal processing stage comprisesa scrambler.
 22. A system as claimed in claim 21 wherein the number ofbits in the multi-bit input to the DAC is greater than the number ofbits in the multi-bit output of the scrambler.
 23. The system of claim22 wherein at least one of the bits of the multi-bit input to thescrambler is coupled to a first logic signal, and at least one of thebits of the multi-bit input to the DAC is coupled to a second logicsignal having a logic state opposite a logic state of the first signal.24. The system of claim 23 wherein there is a predetermined relationshipbetween the first logic signal and the second logic signal.
 25. Thesystem of claim 23 wherein the first logic signal and the second logicsignal do not change logic state.
 26. A system comprising: a digitalsignal processing stage that receives a multi-bit input and provides amulti-bit output; and a switched capacitor DAC wherein the DAC comprisesa switched capacitor network that receives a multi-bit input thatincludes the multi-bit output from the digital signal processing stage,the switched capacitor network having a plurality of sub DACs that eachreceive an associated bit of the multi-bit digital signal, each of theplurality of sub DACs having an associated capacitance that receives anassociated amount of charge in response to the associated bit, the DAChaving an operating state in which at least two of the plurality of subDACs share charge with one another, and having an operating state inwhich less than all of the plurality of sub DACs are connected to anoutput terminal and the switched capacitor network outputs at least oneanalog signal indicative of a sum of values of bits in the multi-bitinput received by the DAC.
 27. The system of claim 26 wherein the DAChas an operating state in which only one of the plurality of sub DACs isconnected to the output terminal and the switched capacitor networkoutputs one analog signal indicative of a sum of values of each bit inthe multi-bit input to the DAC.